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Thread: PSU Power question

  1. #1
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    Question PSU Power question

    Hey guys- I had a question while setting up a grinch and thought that someone might be able to help me.

    I'm going to power the grinch with an old computer power supply. However, I noticed that on the label on the case, it said
    (RED) +5v, 25 amps
    (Yellow) +12v, 10 amps
    (White) -5v, .5 amps
    (Blue) -12v, .5 amps
    and (Black) Ground.

    Why is there a -5 in addition to the +5? Is there a difference between the two? Which one should I use to power a GRINCH?

    * Also, when I measure between +5 and Ground, I get something like 6.3 volts. Is that ok for a Grinch? My multimeter gives me 5v when I measure between -5 and ground.
    Last edited by Drodriguez; 10-22-2008 at 03:03 PM.

  2. #2
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    Default Re: PSU Power question

    The wiki has the answer to the question "is that ok for the Grinch" - http://www.doityourselfchristmas.com...NCH_Controller it will depend on what ICs you are using (half way down the page). 6.3 is a little high, you may need to install a diode to step down the power a bit. There's a thread around here with that info, I'll try and find it.

    As for the + and - question, no idea sorry! You just need the red one, which I think is +. Someone smarter than me probably knows the answer to the + and - question.
    Ugh, this year will be too busy. I'd like to buy a vowel and more time please.

  3. #3
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    Default Re: PSU Power question

    You want the +5 connection. Also, 6.3 looks like it is high, but you are measuring it without any load on the power supply. Normally if you put a load on it, like powering your circuit it will drop closer to the specified 5V.

    Just something to consider.

    Ron

  4. #4
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    Default Re: PSU Power question

    6.3 is a little high, you may need to install a diode to step down the power a bit.
    So can I just use a standard resistor to step it down? I'd rather not blow any more chips.

  5. #5
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    Default Re: PSU Power question

    You need a IN4004 diode - attached is a stunning diagram I did (thank you MS Paint). The yellow box is meant to represent the plug you plug into your Grinch.

    Just to clarify - you need to put the diode in series with the red wire, with the grey strip pointing to the plug.

    Add 1 diode and see what your power drops to. Then and compare it with what your maximum requirements are for the ICs you have.
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    Ugh, this year will be too busy. I'd like to buy a vowel and more time please.

  6. #6
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    Default Re: PSU Power question

    Quote Originally Posted by Drodriguez View Post
    So can I just use a standard resistor to step it down? I'd rather not blow any more chips.

    In simple terms, NO!

    In more detailed terms - NO!

    A resistor will not drop voltage until current starts to flow. With the grinch sitting there with no outputs on the current draw will only be 10 to 20mA (Less if you dont have any LED for power installed), so the voltage drop will be SFA. With all the outputs turned on might give 1 to 2A of load giving a huge voltage drop on the resistor.

    A diode will give a 0.6V (Give or take) voltage drop from 0A through to its max load. An IN4001 is good for 1A, 4004 is 4A and 4007 is 7A - keep half a dozen IN4004's handy for little things like this.

    Also consider getting a 10 ohm 5W resistor and put it across the ground to 5V supply - that will draw roughly 0.5A and should be enough to load the supply up enough to give a good clean voltage out of the supply.
    2011: The year of the pixels, LED's and glowing balls!
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  7. #7
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    Default Re: PSU Power question

    if you connect the red and white wires together, do you go back in time?

  8. #8
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    Default Re: PSU Power question

    Quote Originally Posted by mark View Post
    if you connect the red and white wires together, do you go back in time?
    Only if you are traveling 88 mph............

  9. #9
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    Default Re: PSU Power question

    Quote Originally Posted by mark View Post
    if you connect the red and white wires together, do you go back in time?
    No but if you connect the Red with the White and the Blue your whole economy crashes, hundreds of thousands lose their jobs, and the lights just fade to black.

    Now the question is.... OK who did it?
    2011: The year of the pixels, LED's and glowing balls!
    [url]http://www.lithgowlights.com/[/url]

  10. #10
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    Default Re: PSU Power question

    Quote Originally Posted by daviddth View Post
    No but if you connect the Red with the White and the Blue your whole economy crashes, hundreds of thousands lose their jobs, and the lights just fade to black.

    Now the question is.... OK who did it?
    All the more reason to make sure OUR lights stay on. It's the big fish that messed up the ecomony in pursuit of greed.

    It's the little fish that need to see there's still light.

    Let there be lights!
    Last edited by Ronp; 10-27-2008 at 08:36 PM. Reason: hmmm
    Cheers!
    Steve

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